This invention relates to a mold-making silicone rubber composition of addition reaction cure type for use in the replication of cement material, and more particularly, to a mold-making silicone rubber composition which cures into a rubber form and is suited for use in operation of making molds requiring a high level of mold release, typically for molding of trial manufacture models or prototype molding, or for use in the replication of cement material for forming pseudo-rocks or the like.
As used herein, the term “mold-making composition” refers to an uncured composition having fluidity in the uncured state which is brought into contact with the entire surface or a surface of a master pattern by such a technique as casting or coating and then cured in that state to form a mold which is used in the subsequent production of replicas using a resin or the like. The term “mold release” refers to not only release of the cured mold from the master pattern, but also release of replicas from the mold.
In the prior art, silicone rubber has been widely used in a variety of fields while taking advantage of its excellent properties including heat resistance, freeze resistance and electrical properties. Especially due to its smooth mold release, the silicone rubber is also used as mold-making composition. While prototype molding is adopted at the stage of commercial product development or product sample manufacture in the fields of electronic equipment, business machines, household appliances, automobile parts and the like, liquid silicone rubber compositions of addition reaction cure type are often used in the prototype molding because of the attractive advantages that they are effective in reducing the cost and requisite time of prototype molding, and especially, in improving the working efficiency. Also in the replication of pseudo-rocks or the like, liquid silicone rubber compositions of addition reaction cure type featuring high strength are used in order to reproduce a complex shape reversal.
When cement is molded for the replication of pseudo-rocks or the like, however, a whitening phenomenon that the cement surface discolors and a water-repelling phenomenon that the surface becomes water repellent occur under the influence of calcium hydroxide contained in the cement. It is desired to overcome these problems.
JP-A 2001-288370 discloses a resin composition comprising 10 to 60% by weight of a resin and 40 to 90% by weight of inorganic particles mainly composed of silicon. Coal ash is added to the resin in the resin composition. JP-A 2002-338812 and U.S. Pat. No. 6,780,919 disclose an addition curing type mold making material. However, these silicone rubbers for cement molding which can control generating of discoloration on the surface of cement were not offered.